1. Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for electrochemical mechanical processing.
2. Description of the Related Art
Electrochemical mechanical planarizing (ECMP) is a technique used to remove conductive materials from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion compared to conventional planarization processes. ECMP systems may generally be adapted for deposition of conductive material on the substrate by reversing the polarity of the bias. Electrochemical dissolution is performed by applying a bias between a cathode and a substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte. Typically, the bias is applied to the substrate surface by a conductive polishing material on which the substrate is processed. A mechanical component of the polishing process is performed by providing relative motion between the substrate and the conductive polishing material that enhances the removal of the conductive material from the substrate.
Copper is one material that may be polished using electrochemical mechanical planarizing. Typically, copper is polished utilizing a two-step process. In the first step, the bulk of the copper is removed, typically leaving some copper residue projecting above the substrate's surface. The copper residue is then removed in a second, or over-polishing, step.
However, the removal of copper residue may result in dishing of copper features below the plane of a surrounding material, typically an oxide Or a barrier layer of other materials, such as TaN, and the like. The amount of dishing typically is related to polishing chemistries and processing parameters utilized in the over-polish step, along with the width of the copper features subjected to polishing. As the copper layer does not have a uniform thickness across the substrate, it is difficult to remove all the copper residue without causing dishing over some features and not removing all of the copper residue over others. However, at the present time, it is difficult to perform both bulk and residual material removal at a single polishing station. Thus, it would be advantageous to perform bulk and residual material removal on polishing stations optimized for those processes to enhance substrate throughput while providing copper residue removal and minimized dishing.
Thus, there is a need for an improved method and apparatus electrochemical mechanical planarizing.